What numbers to believe?

[blkvette94]

I desperately need a question answered (googled, forums, No luck on an answer out there). My question is regarding the readings I am getting from HP Tuners (and the car??). Which reading do I believe-- the HP Tuners trans slip pid or the math?

Details---------------------
VCM Suite Product: VCM Scanner 4.8.7

I have a 17 Chevy SS with 6l80e with roughly 33,000 miles on it. Less than 5,000 miles with serious modifications. I have swapped to the 6l90 converter and made changes to the transmission programming via HP tuners (up pressures 20%, reduced shift times 10%, volume presets, etc.). Nothing drastic, just a few bumps here and there.

The issue------------
The computer/HP Tuners has a trans slip Pid showing as [4117.56] for my car. During my shifts I can get huge trans slip numbers based on the computer provided trans slip pid. Yet when I go old school math and use other pids to measure slip ((Trans input speed [4110.56] divided by selected gear ratio [4221]) minus trans output speed [4111.56])--- I get very little slip indicated. For example, the trans slip pid shows 1179.6 rpm but the math shows 6 rpm.

To me, during the shifts, 1000 plus slip is an issue. However, I am not worried about 6RPM slip during a gear change with .23 second shift time under mild acceleration. The indicated slip for both goes away after shift is completed during normal cruise (randomly from plus 20ish to negative 20Ish indications).


So again what numbers do I believe? Indicated trans slip or old school math?

[grandam75]

I think 1000-1300rpm is normal. I would not focus on the actual slip rpm as much as if it is increasing before/during/after the shift. It should show slip as the old clutch releases and new applies but go up fast and stay around the same slip rpm. Then drop off fast. If it continues to rise or spikes there is a problem.